Reclaiming the Value of Urine for Agriculture

What is the potential for reclaiming the phosphorus present in human urine for agricultural use? World-wide there are a number of projects exploring this question, but few in the United States.[1] A small-scale but exciting example is the Rich Earth Institute’s Urine Nutrient Reclamation Project (UNRP) in Brattleboro Vermont. Since 2012, Rich Earth has been collecting urine from 150 – 200 households in the community, transporting and sanitizing it, and using it as fertilizer on test fields of hay and vegetables. Rich Earth currently invites participants to save urine at home and bring it to a central depot. The long-term goal, however, is to support the wide-spread use of simple toilets and storage systems that can divert urine from aging sewage, storm water and water treatment systems, many of which are underperforming in cases of extreme weather events and changes in water cycles due to climate change. Urine accounts for roughly three-quarters of the nitrogen and roughly half of the phosphorus in municipal waste streams. Research Director Abe Noe-Hays estimates that one thousand gallons of urine contains the equivalent of 109 pounds of urea, 13 pounds of triple superphosphate, and 29 pounds of muriate of potash (KCl), as well as smaller amounts of calcium, magnesium, sulfur and micronutrients Therefore, substituting urine for chemical fertilizers can be an appealing prospect depending on the nutrient needs of specific crops and the nutrient status of soils.

Rich Earth’s field tests on hay over several years have shown equivalent yields between urine-fertilized and chemically-fertilized test plots, both significantly higher than unfertilized plots. Forage quality remained high, and one farmer has been able to achieve a solid second cutting of hay where previously yields were not sufficient to warrant a second cutting. Farmers participating in the project have had good results applying the sanitized urine to hayfields without dilution; one of Rich Earth’s goals is to develop a concentrated product that can be applied directly to reduce labor requirements. While it is likely the nitrogen rather than the phosphorus from urine is what has been the most significant nutrient in these Vermont test fields (because the soils were not deficient in phosphorus at the start), these experiments are an important model for the potential of recycling human waste for fertilizer world-wide.

Among hay and vegetable farmers in New England that Rich Earth has surveyed, interest in the potential of a urine-derived fertilizer is high, although farmers are cautious. Respondents wrote, for example, “I think it is a great way to start closing the nutrient cycle – counting humans as part of the whole environmental web,” and “Could be a silver bullet; cost effective, renewable, recycling,” and “It’s about time we started using this valuable nutrient in the field instead of allowing it to contaminate drinking water by flushing it down the toilet.” Research suggests that farmers who currently practice organic or ecological methods may be more open to using urine than conventional farmers, but they may also have more concerns about potential contaminants in the urine including their impact on the health of soil biota. Not surprisingly, many also express concerns about how their customers may respond to the use of urine-derived fertilizers on their crops.

Rich Earth’s research aims to respond to some of these concerns. The organization will assess farmer interest and technical needs with regard to using these fertilizers on animal feed and fiber crops, perennial crops (such as fruit trees), ornamentals and other non-edible and edible crops. Testing indicates that heavy metal levels are extremely low – on average a thousand times below accepted risk levels. And although fiber, biomass, and animal feed crops could utilize all urine-derived fertilizer for the foreseeable future, Rich Earth has conducted field studies with lettuce and carrots to examine the fate of pharmaceuticals as well as biological components (viruses and bacteria) when urine-derived fertilizers are used for growing edible crops. Final results from this research have not yet been published, but the data so far indicate that while trace levels of pharmaceuticals could be detected in both lettuce and carrot tissue, the levels were very low. As Noe-Hays puts it, “a person would have to eat a salad from the study plot every day for two thousand years to get a single dose of acetaminophen (Tylenol).” With regard to bacteria and viruses, this research is ongoing, but current standards specify that urine can be effectively sanitized by pasteurization or by storing it from one to six months before using. Rich Earth’s ongoing research will help to better understand what happens under different storage and treatment practices.

With regard to public perceptions, Rich Earth’s social research seeks to learn more about what people know and think about what happens to their waste currently, and discover the most useful communication strategies to help attitudes evolve. In surveys and interviews with people who have contributed urine to the UNRP over the last four years, one important message stands out: people can and do change their attitudes over time. Although sometimes reluctant and uncomfortable at first, participants have become more and more enthusiastic about saving their urine and seeing it reused for agriculture. Learning about the value of urine as a fertilizer has inspired much of this evolution. For example, one person said, “I am so impressed by this simple process that turns a waste product into something so useful, saves water and avoids chemical fertilizers in our soil. Amazing! I love the environmental education that happens when curious visitors ask about that weird jug in our bathroom. It has started some good conversations!”

Of course there are no “weird jugs” when simple urine-diverting toilets are employed. Rich Earth is working towards more wide-spread use of these systems for source-separation and nutrient reclamation from urine, including addressing regulatory issues. Until now, human waste has been seen by regulatory agencies as something to be “disposed of” so as to protect public health. But Rich Earth sees urine is a resource. Rather than needing to be “disposed of,” it should be collected and made use of as a “value-added” product. The organization currently has a permit for a mobile-pasteurizing unit through the Vermont Agency of Natural Resources’ Watershed Management Division. This has allowed local regulators to become comfortable with the concept of recycling urine for fertilizer. Using this permit, Rich Earth has developed the tools and equipment needed for larger scale processing of urine.

Ongoing research, now funded with a four-year grant through the National Science Foundation, will allow the organization to learn more about what regulators need to know and how best to communicate with them so that regulations can be written that will protect human health and the environment by keeping urine out of the waste stream and returning it to the soil. Step by step, community by community, it will then become possible to close the loop and recycle the abundant nutrients, such as phosphorus, that we so generously expel in liquid form every single day.

Opinions expressed here do not necessarily reflect those of the Sustainable Phosphorus Alliance.

Tatiana Schreiber is an independent scholar with a doctorate in Environmental Anthropology. She teaches in the areas of agroecology, environmental studies and writing at Keene State College in New Hampshire and is a research associate at Rich Earth Institute. She also operates Sowing Peace Farm in Vermont, selling organic seedlings of heirloom and unusual varieties of vegetables and medicinal plants. Contact her at tatiana@richearthinstitute.org